/*
 * ExponentialGrowth.java
 *
 * Copyright (C) 2002-2006 Alexei Drummond and Andrew Rambaut
 *
 * This file is part of BEAST.
 * See the NOTICE file distributed with this work for additional
 * information regarding copyright ownership and licensing.
 *
 * BEAST is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 *  BEAST is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with BEAST; if not, write to the
 * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
 * Boston, MA  02110-1301  USA
 */

package dr.evolution.coalescent;

/**
 * This class models an exponentially growing (or shrinking) population
 * (Parameters: N0=present-day population size; r=growth rate).
 * This model is nested with the constant-population size model (r=0).
 * 
 * @version $Id: ExponentialGrowth.java,v 1.7 2005/05/24 20:25:56 rambaut Exp $
 *
 * @author Alexei Drummond
 * @author Andrew Rambaut
 */
public class ExponentialGrowth extends ConstantPopulation {

	/**
	 * Construct demographic model with default settings
	 */
	public ExponentialGrowth(int units) {
	
		super(units);
	}

	/**
	 * returns growth rate.
	 */
	public final double getGrowthRate() { return r; }
	
	/**
	 * sets growth rate.
	 */
	public void setGrowthRate(double r) { this.r = r; }
	
	/**
	 * An alternative parameterization of this model. This
	 * function sets growth rate for a given doubling time.
	 */
	public void setDoublingTime(double doublingTime) { 
		setGrowthRate( Math.log(2) / doublingTime );
	}
						
			
	// Implementation of abstract methods

	public double getDemographic(double t) {
		
		double r = getGrowthRate();
		if (r == 0) {
			return getN0();
		} else {
			return getN0() * Math.exp(-t * r);
		}
	}

	public double getIntensity(double t)
	{
		double r = getGrowthRate();
		if (r == 0.0) {
			return t/getN0();
		} else {
			return (Math.exp(t*r)-1.0)/getN0()/r;
		}
	}
	
	public double getInverseIntensity(double x) {
		
		double r = getGrowthRate();
		if (r == 0.0) {
			return getN0()*x;
		} else {
			return Math.log(1.0+getN0()*x*r)/r;
		}
	}
	
	public int getNumArguments() {
		return 2;
	}
	
	public String getArgumentName(int n) {
		if (n == 0) {
			return "N0";
		} else {
			return "r";
		}
	}
	
	public double getArgument(int n) {
		if (n == 0) {
			return getN0();
		} else {
			return getGrowthRate();
		}
	}
	
	public void setArgument(int n, double value) {
		if (n == 0) {
			setN0(value);
		} else {
			setGrowthRate(value);
		}
	}

	public double getLowerBound(int n) {
		return 0.0;
	}
	
	public double getUpperBound(int n) {
		return Double.POSITIVE_INFINITY;
	}

	public DemographicFunction getCopy() {
		ExponentialGrowth df = new ExponentialGrowth(getUnits());
		df.setN0(getN0());
		df.r = r;
		
		return df;
	}

	//
	// private stuff
	//

	private double r;	
}
